Portugal great Eusebio is set to stay in hospital over Christmas after being diagnosed with double pneumonia.
Doctors at the Hospital da Luz in Benfica are optimistic that the 69-year-old will make a full recovery.
Joao Sa, head of the intensive care unit, said the illness requires close monitoring and Eusebio will undergo treatment for several days.
Eusebio scored 41 goals in 64 games for Portugal and was named one of the 10 best players of all time by Fifa.
The Portuguese Football Federation said in a statement: "We wish a speedy recovery to Eusebio and also to express that the whole of the Portuguese football family is behind him.
"It will take a lot of strength to overcome this difficulty, but he has honoured Portugal for many years with his distinguished presence."
Born in Mozambique when it was still a Portuguese colony, Eusebio da Silva Ferreira became a national icon for his powerful performances in the 1960s for Benfica and Portugal.
Nicknamed 'The Black Panther' and 'The Black Pearl', he won 10 league championships, five Portuguese cups and one European Cup in his 15 years at Benfica and was Portugal's top league scorer between 1964 and 1973.
Benfica said in a brief statement: "Benfica wish a speedy recovery to the Black Panther."